Introduction

"What do hummingbirds eat?" is a question often asked of hummer enthusiasts. It's a simple question, and you'd think the answer would be simple too. But hummingbirds are an enigma. They are among the most studied families of birds, yet every time we think we know all there is to know about their habits, they do something that flies in the face of that knowledge. What they eat is a case in point.

Seeing hummingbirds flit from flower to flower, early naturalists presumed the birds were getting liquid nourishment in the form of nectar from the blooms, just as bees do. This, they thought, was all the birds ate.

This reasoning, however, had its detractors. Some proposed that the hummingbirds weren't visiting the flowers for nectar-they believed the birds were instead going for the minute insects hidden inside the blooms. Supporting this position were numerous observations of the birds hawking gnats and other small insects from the air.

Added to this was the fact that those aviculturalists that tried keeping hummers in captivity found that the birds did not live long on a diet of only sweets; indeed, those hummingbirds that had access to sources of protein fared well in confinement. The reason they drank sugary fluids at all, according to some, was because confined birds were apt to consume foods they wouldn't naturally eat in the wild.

All of these circumstances led to the theory that the majority of the birds' food consisted of invertebrates. Any nectar ingested, therefore, was merely a consequence of the birds foraging on flowers.

The Insect-only Rationale

To settle the question of what, exactly, hummingbirds eat, early ornithologists shot a number of thema perfectly legal activity in those daysin order to examine the contents of their stomachs. Upon dissection, they discovered the remains of such prey as flies, gnats, wasps, aphids, beetles, leafhoppers, and spiders, often completely packing the abdominal cavity. Zoologist and museum director Frederic A. Lucas found that the stomach of one hummingbird "contained remains of not less then 50 individuals, probably more."

What he and other scientists didn't find, however, was nectar. Because of this, small invertebrates appeared to be the answer to what comprises the birds' diet. For these researchers, the case was closed.

There were flaws in this insect-only rationale, however. For one thing, the stomachs of some hummingbirds were empty, even though the birds had been seen foraging not long before their demise. What the ornithologists of the time didn't realize is that nectar and other liquids are digested quickly and thus are nearly impossible to detect in the stomach. This is especially true for hummers because their stomachs have an unusual structure. As hummingbird expert Walter Scheithauer describes it, "the outlet does not lie below as in other birds, but above, directly alongside the entrance to the stomach. The nectar can flow direct to the intestine without passing through the stomach."

Positive proof that sugary fluidsand therefore nectarare an essential part of a hummingbird's diet came when people started placing containers filled with sweetened water outdoors. Despite access to all the bugs they could eat, the birds still eagerly drink the liquid at hummingbird feeders.

Artificial feeders also proved that hummingbirds weren't limited to eating only invertebrates and nectar, because honey or sugar mixed with water were both used as replacements for nectar. (Today most experts consider plain white table sugar to be the best nectar substitute for the birds, and discourage using honey or other sweeteners in hummingbird solutions.)

Of course, nectar, honey, sugar, and insects aren't the only things hummingbirds consume. Some hummingbird stomachs were also shown to contain grains of pollen. The stomachs of two blue-throated hummingbirds examined by biologists Clarence Cottam and Phoebe Knappen included 10 percent and 15 percent pollen. Whether this foodstuff is ingested intentionally, or is merely a consequence of sipping nectar, is not known.

Tree Sap

It is known, however, that most hummingbirds also drink tree sap. Records of hummingbirds drinking from sap wells date back to at least the 1880s. Tree sap, it turns out, is an ideal alternative to nectar. Like nectar, sap is commonly composed of sucrose, water, and amino acids in relatively the same proportions. Because of this, hummingbirds have developed close associations with sapsuckers. It is believed that ruby-throated and rufous hummingbirds time their spring migration northward to follow that of the sapsuckers. In Canada and the northern United States, these hummingbirds arrive on their nesting grounds several weeks before any flowers are in bloom. The hummers are able to acquire all the energy they need from the sap produced from the efforts of sapsuckers.

This affiliation with sapsuckers continues throughout the rest of the year as well. Rufous, ruby-throated, broad-tailed, and Calliope hummingbirds have been found nesting near sapsuckers' sap wells, and some hummers follow their meal tickets from drill site to drill site to learn the location of each. Hummingbirds have even been observed defending the sapsuckers' feeding trees against other birds.

Sap wells also provide fall-migrating hummingbirds with much-needed refueling stations, where the birds may spend as long as a week before continuing south. Even during winter, hummers depend on the sapsuckers' borings to supply much-needed sustenance.

A favorite sap of the hummingbirds is that of the sugar maple treethe same substance from which maple syrup is made. Several researchers have offered maple syrupthe boileddown sap, not the artificial stuffto hummers over the years to observe the birds' reaction to it, with positive results. The birds readily take to the sweet drink.

Fruit Juice

Hummingbirds are also known to sip the juice of over-ripe or previously pecked fruits. One might assume they are merely going after insects attracted to the fruit, but an early account shows that this is not the case. In an 1894 article in The Auk, Janet L. Hine wrote about observations made of a rubythroat, saying, "In our neighbor's orchard a hummingbird sucked juice from an apple while a young girl was in the act of paring it."

This is not the only record of hummers eating the juice of apples and other fruits. Several species of hummingbirds find the sweet fluid of persimmons appetizing; Anna's hummingbirds seem especially fond of the juice, and there have been numerous sightings of them at these fruits. Pears, oranges, and prickly pears are a few more of the fruits whose juice may attract hummingbirds. Drinking the juices of fruits has been witnessed enough times that it is no longer considered an unusual occurrence.

Sugary Emissions from Trees and Insects

Hummingbirds do still have some gustatory surprises for us, however. In August of 1981 in Colorado Springs, Colorado, researchers Peter Kevan, Sherrane St. Helens, and Irene Baker noticed several rufous and broad-tailed hummingbirds hovering beneath the ends of some Gambol oak branches, lapping a substance seeping from them. The source of the discharge turned out to be a number of bacteria-induced lesions on the twigs. Upon examination, the biologists found the secretion from the wounds to be similar to the nectar of flowers the birds visita high ratio (1.117) of sucrose to glucose and fructosebut it had a larger concentration of amino acids than the flowers' nectar.

This effusion is not a conventional source of nourishment for hummers, because normally it quickly evaporates and hardens when exposed to the sun. In this particular circumstance, however, it had rained the evening before, and the weather that morning was still damp and cloudy, allowing the substance to remain in a liquefied form that the hummingbirds could readily consume.

Because hummingbirds have a sugar-centric lifestyle, it makes sense for them to be drawn to a sweet substance secreted from the wounds of trees, and it stands to reason that they would likewise be enticed by sugary excretions from insects. There have, in fact, been a number of such observations. On several occasions the birds have been seen ingesting honeydew exuded through filaments protruding from the bark of trees, which, upon close examination, were shown to be coming from scale insects. Each filament produced a small drop of clear, sweetish liquid at the outer tip, which the hummingbirds eagerly devoured. Of course, scales aren't the only insects to manufacture honeydewaphids also make it, and there is at least one report of hummingbirds eating the sugary emission from them as well. Considering the sweetness of the secretions emanating from these insects and tree lesions, it's not hard to see why hummingbirds would add them to their diet. That's not true for everything they eat, however. Some of the substances they consume do seem to be well out of the realm of their normal fare.

Sand, Ashes and Seawater

Various species of hummingbirds, on numerous occasions, have been seen sticking their bills into such things as sand, wood ashes, and seawater. Those who witnessed these events were certain the birds were not eating insects, but were indeed ingesting the item itself. Why would the hummers do this? All of these unusual foodstuffs tend to be high in calcium and may also contain sodium and other minerals. Because the majority of birds noted were femaleat least in those instances where the sex of the hummer was mentionedit has been proposed that the reason for this activity is to replace the calcium and other minerals lost during egg production.

Ashes, sand, seawater, secretions from insects, pollen, and the fluids of fruits and other plant parts are a far cry from the nectar and bugs that were once believed to be the hummers' only sources of nutrition. There are undoubtedly even more items out there that the birds feed onthings that will once again change our idea of what hummingbirds eat.

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